How does the situation change for excess radiation investigated at ultra-relativistic collision energies?
Continuing clockwise in Fig. REF , the respective mass distributions are depicted for collisions at SPS at an beam energy of \(\sqrt{s_{\mathrm {NN}}}\, = 158 \, \mathrm {G}e\mathrm {V}\)  for the case of dielectrons (CERES) and dimuons (NA60), where the latter data is compared with two different types of model calculation (shown in the bottom row).
The CERES spectrum is compared to a calculation based on thermal emissivities [1]} using the isentropic expansion model.
While the statistical precision of the CERES spectrum is just about good enough to discriminate between a scenario with (labelled as “total”) and without including coupling to baryons (“no bar \(\rho \) ”), yet the data point at 150  M\(e\) V/\(c^{2}\)  seems to support the observation of HADES of a strong excess yield at low-masses due to the \(\rho \mathrm {N}\leftrightarrow N^*\)  loop in the \(\rho \)  in-medium self energy.
Contributions from Drell-Yan and QGP radiation are not subtracted here but seem to contribute little as can be appraised from the respective contributions also shown in the theory cocktail (DY, QGP).
The model calculation also suggests little contributions due two multi-pion annihilation (\(4\pi \)  mix).
